As the field of fine color photography becomes more mature, a greater appreciation for the loss of print quality due to environmental degradation through aging has been realized. Various print coatings and laminating materials have been tried in an attempt to provide protection which is effective in extending the life of photographic prints. The fading of photographic prints is a continuously progressive process, principally caused by ultraviolet radiation, cycling relative humidity, high temperature, atmospheric pollution, and oxidation. Print degradation is significant in the two most common processing systems, namely, dye bleaching and chromogenic development. Photographic degradation is particularly acute with chromogenic development.
Various specific solutions to the problems of preserving photographic prints have been developed to achieve a very long life or "archival" storage of photographs. These include the use of print lacquers, plastic laminates, spray coatings, and UV-absorbing plastic filters. In his book, entitled "The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures" (Preservation Publishing Co., Grinnell, Iowa, 1993), Henry Wilhelm describes the effects of each of these preservation methods in great detail. As this reference explains, many of the commercially-accepted techniques for extending the life of photographic prints may actually reduce the light stability of the photographs, rather than extending it.
Many of the large photographic companies have spent great effort testing materials and methods for preserving their products. One such study was published by the Ilford Company of Fribourg, Switzerland, in July of 1987, entitled "Technical Service Information 2-87". This publication describes the various methods for best preserving their products. These tests indicate that holding color photographs between glass plates was not effective in preserving the light stability and that the most effective method was embedding photographic prints in a liquid plastic, which is then cross-linked by UV or moderate heat to form a solid sheet. The embedding materials tested were SPECTRALITE and DUROLITE polyester resins. Embedding is not a readily available technique since special equipment and skill are required and it is only normally performed by specialized firms. This publication also confirms that without protection, typical photographic prints, such as the Ilford CIBACHROME II prints, only have a life expectancy in low light, indoor conditions of from 10-15 years.
While not applicable to photography, it is also known to laminate colored inks printed on a polyurethane interlayer between glass plates, the polyurethane being both the printing substrate and the bonding material. This method of creating an architectural graphic glass structure is described by the applicant in his previously issued U.S. Pat. No. 4,968,553. It is also commonly known to heat-seal portrait photographs between opposing sheets of plastic, such as polyvinyl chloride (PVC). This process is used for making personal identification cards, however, it is unacceptable because the PVC continues to harden as it ages and often cracks and yellows. Such a process is disclosed in U.S. Pat. No. 4,768,811 issued to Oshikoshi et al.
U.S. Pat. No. 4,378,392, issued to Segel, shows a photographic preservation laminate composed of a transparent film of ultraviolet-stabilized polyurethane terephthalate or ultraviolet-stabilized acrylonitrile and a transparent silicone or acrylic adhesive bonded to the film, the laminate being adapted to be bonded to the image surface of the photograph by the adhesive. This reference also discloses that to provide even greater protection, an additional layer of transparent fluorocarbon polymer may be bonded to the other laminated materials with a silicone or acrylic adhesive.
There is therefore a need in the art for a method of obtaining archival preservation of photographic prints which is effective, readily available, and economical.